Critical behavior of the ionic system n-Propyl-tri-n-butylammonium iodide + water near its upper and lower consolute points
✍ Scribed by M. Kleemeier; W. Schröer; H. Weingärtner
- Book ID
- 104303900
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 643 KB
- Volume
- 73-74
- Category
- Article
- ISSN
- 0167-7322
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✦ Synopsis
Aqueous solutions of tetraalkylammoniurn salts, &NX, with sufficiently large chain length of the alkyl groups (R23) show liquid-liquid itmniscibilities at elevated temperatures. In general, upper consolute points are observed, but the shapes of the miscibility gaps indicate the existence of lower consolute points suppressed by crystallization. In aqueous solutions of the unsymmetrically substituted salt n-propyl-tri-n-butylammonium iodide (PrBusNI) the lower consolute point is shifted above the crystallization curve, so that the closed miscibility gap can be monitored completely. We have performed accurate measurements of the coexistence curve near both the lower and upper consolute points of this system. The upper critical point lies at approximately 345.73 K and 0.438 in weight fraction of the salt. The lower critical point lies at 331.72 K and 0.446 in weight fraction. In the vicinity of the critical points an Ising-like critical behavior of the coexistence curve is found. The correct critical exponent of the Ising model is however only observed, if account is made for the peculiarities of re-entrant phase transitions with upper and lower critical points close to one another. The results are discussed with regard to recent observations of an apparent meanfield-like behavior of some ionic fluids. * Dedicated to Prof. Dr. Josef Barthel on the occasion of his 68th birthday and retirement.